[MIR] Fix cyclic dependency of MIR formatter

Summary:
Move MIR formatter pointer from TargetMachine to TargetInstrInfo to
avoid cyclic dependency between target & codegen.

Reviewers: dsanders, bkramer, arsenm

Subscribers: wdng, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D72485